How It Works – Electric vehicle batteries

Development of energy storage hasn't kept pace with the car, but new technologies are on the horizon

Hybrids and electrics are generally known as “green” vehicles, because they either burn less fossil fuel compared to non-hybrids, or in the case of battery-powered vehicles, none at all.

Still, there’s an environmental cost associated with them. Their batteries contain numerous chemicals, while lithium, commonly used in them, is most abundantly found in Bolivia, Argentina, Chile, and China, as well as Australia – perhaps with the potential of creating lithium cartels in place of the oil variety. Increased vehicle electrification and the use of cobalt in batteries has also rekindled interest in the mining town of Cobalt in northern Ontario, bringing a double-edged sword of economic recovery versus environmental issues.

Electric vehicles (EVs) are primarily a niche market because of their range and recharging time, but that’s not necessarily because of the cars themselves. They’ve actually been around since the late 1800s, and were often a popular choice when their pushbutton operation was much easier than hand-cranking a gasoline car.

The flat battery pack spans the entire length of the Chevrolet Bolt’s floor and is integrated into the chassis.GM Canada /
Driving

Today’s sophisticated electronics systems have considerably improved electric cars, but it’s the battery technology that hasn’t kept pace. There’s still a limit to how much energy they can store, and in many cases, you need a bigger battery to get longer driving range. That adds cost and weight – and the more weight, the more power it takes to move it. Ironically, that larger battery actually cuts into the extra range it provides.

Early electric cars used lead-acid batteries because that’s all that was available, but they’re too heavy and inefficient for EVs compared with modern alternatives. They’re still found in conventional cars, where they’re used to start the engine. They contain a negative lead plate and positive lead-dioxide plate, both submerged in a bath of sulphuric acid and water. A chemical reaction produces the voltage. The battery only stores electricity, and when the car is running, it’s recharged by the alternator, which also powers the lights and other electrical systems.

Instead, electrified vehicles generally use nickel-metal hydride (NiMH) or lithium-ion (Li-ion) batteries. NiMH batteries were used to power earlier electric cars, such as GM’s EV-1 in 1999, but today they’re primarily used in some hybrids to power an electric motor alongside a gasoline engine. They’re not as energy-dense as Li-ion, but they’re also less costly, and they aren’t affected as much by extreme temperatures. They contain negative and positive electrodes made of nickel alloy, and hydrogen stored as solid metal hydrate. In a hybrid, they’re charged through regenerative braking, using kinetic energy otherwise lost during deceleration, which is converted and stored as electricity.

In most electric vehicles, and some hybrids, lithium-ion batteries have pushed NiHM to the curb. Li-ion battery cells contain electrodes made of metal alloy and carbon-based material such as graphite, and their electrolyte contains lithium ions. Like other vehicle batteries, they store energy rather than make it – they have to be recharged, of course – and the lithium ions flow from the negative electrode to positive when the vehicle needs energy to operate, and from positive to negative when the battery is being charged.

Its higher energy density means a Li-ion battery weighs less than a NiMH battery of the same capacity – in the 2018 Toyota Prius, which offers both types, the Li-ion pack weighs some 16 kilograms less than the NiMH. While batteries slowly discharge on their own if they aren’t used for a while, Li-ion holds its charge almost twice as long as NiMH. They require no maintenance, but on the down side, Li-ion batteries don’t like extreme temperatures, and require thermal management systems so they don’t get too hot or too cold. They also need protective circuits to prevent them being overcharged or excessively drained, and while their costs have come down, they’re still relatively pricey.

An increasing number of vehicles use lithium-polymer batteries, which work the same way as Li-ion but have gelled electrolyte. The cells are lighter and they’re flexible, making them easier to package in the battery.

Competition and volume production are bringing down prices, and companies like Tesla and Panasonic are ramping up battery manufacturing. According to market analyst Bloomberg, battery prices were around $1,300 per kilowatt-hour in 2010, but by 2016, they’d dropped to $350, and the company forecasts that by 2025, they could be as low as $130.

Lead-acid batteries are about 95 per cent recyclable, including their acid, and NiMH batteries contain metals that make them worth recycling. Li-ion batteries can also be pulled apart for their metal, but while lithium is recyclable, the process currently makes it more costly than using virgin material. However, since Li-ion batteries still have a lot of life left in them after they’re too degraded for use in vehicles, several companies – including some automakers – are finding ways to use them for home or industrial storage, such as in conjunction with solar panels.

So what’s next? Several companies are working to develop solid-state batteries, which use high-capacity electrodes and solid electrolyte and could have two to three times the energy capacity of Li-ion. And there’s even the possibility of supercapacitors, which quickly store and release energy, and which might one day eliminate batteries altogether.